1. Field of the Invention
The present invention relates generally to local administration of therapeutic agents, and more particularly, to bone and/or tissue scaffolding for delivery of therapeutic agents.
2. Related Art
Implantable medical devices are widely accepted and used in several applications such as microelectronic implants, for example, cardiac implant stimulators, neurostimulators, etc., and musculoskeletal and orthopedic implants, for example, hip, knee, and other joint replacements, etc. Due to improvements in medical implant technologies and the demographics of recipients, these medical implants have been in use are being used for many decades.
Such implants are often made of rigid materials and are in contact with the more flexible surrounding bone and tissue, which over time cause the implant to loosen. Loosening of the implant compromises the ability of the implant to perform its intended function and can be painful to the implant recipient. In situations where loosening occurs, the implant will often have to be replaced. To prevent loosening, several materials have been developed over the years. One type of material, commonly referred to as in-growth scaffolding, is a porous material having an open-celled structure to allow the surrounding bone or soft tissue to advance into the pores, which anchors the implant to the surrounding tissue. In the case of traditional orthopaedic implants, the in-growth material allows osteointegration between the implant and bone.
In addition to loosening, other problems that develop with implants over time include disease, infection, inflammation, etc. While porous in-growth scaffolding material provides a mechanism for integration of the device, such material cannot prevent diseases, inflammations, infections, etc., of the bone and tissue surrounding the implant. One source of such disease, inflammation and infection is from polymer debris shed from the implant and absorbed by the recipient. Also even with scaffolding materials, the surrounding bone tissue may require growth promotion therapies. Further, if there is a need to treat the bone and tissue surrounding the implant with a pharmaceutical or biological agent, conventional scaffolding does not provide the ability to provide such treatment.